JPH10297016A - Optical beam scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical beam scanning optical device excellent in image quality in which image density can be switching without requiring any movable mechanism. SOLUTION: The laser diode element 3 in a laser diode array constituting the light source unit for an optical beam scanning optical device has three emission points 3a-3c interval of which is not constant in the subscanning direction. At the time of switching the image density, two emission points are selected arbitrarily out of three emission points 3a-3c by means of the emission point controller and at least any one of the deflection speed of a polygon mirror or the rotational speed of a photosensitive drum is altered by means of a speed controller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning optical device, and more particularly to a light beam scanning optical device used as an image writing means of a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art As a light beam scanning optical device, a plurality of light beams are simultaneously focused on different positions on a surface to be scanned.
It is known that a plurality of lines are simultaneously written in one scan. In this type of apparatus, when switching the image density, a method of switching the interval between light beams by moving a prism or the like disposed before the light beam coupling element along the optical path (for example, Japanese Patent Application Laid-Open No. No. 68016) or a method of switching the interval between light beams by rotating a light source (for example, see Japanese Patent Application Laid-Open No. 56-104315).
Has been proposed.

[0003]

However, in the conventional light beam scanning optical device, it is necessary to move the prism of the movable portion or rotate the light source with an accuracy of the order of 0.1 μm, and the position control is difficult. There was a problem that it was extremely difficult. Further, when the distance between light beams is switched by moving a prism or the like, there is a problem that a laser diode array having a plurality of light emitting points cannot be used as a light source. This is because a prism or the like that switches the interval between light beams needs to be arranged before the light beam combining element along the optical path, whereas the light beams emitted from each light emitting point of the laser diode array are already mutually This is because they are close to each other and a prism or the like cannot be arranged on the optical path.

Therefore, an object of the present invention is to switch the image density without using a movable mechanism, and
An object of the present invention is to provide a light beam scanning optical device capable of obtaining excellent image quality.

[0005]

In order to achieve the above object, a light beam scanning optical device according to the present invention comprises: (a) a light source having at least three light emitting points arranged at different positions in the sub-scanning direction. (B) a light emitting point switching means for selecting two light emitting points from the light emitting points to emit light to switch the image density, (c) a deflector for deflecting and scanning a light beam emitted from the light source, (d) a scanning surface to be irradiated with the light beam and moving in the sub-scanning direction; (e) a scanning optical element for causing the light beam emitted from the deflector to scan the scanning surface in a line shape; A) speed changing means for changing at least one of the deflection speed of the deflector and the moving speed of the surface to be scanned in order to switch the image density. Here, the light emitting point intervals of the light source are equal or unequal in the sub-scanning direction.

[0006]

According to the above arrangement, according to a desired image density,
The light emitting point is switched by the light emitting point switching means, and at least one of the deflection speed of the deflector and the moving speed of the surface to be scanned is changed by the speed changing means. The light beam interval is changed by combining the switching of the light emitting point and the change of at least one of the deflection speed of the deflector and the moving speed of the surface to be scanned.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a light beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings. In FIG. 1, the light beam scanning optical device generally includes a light source unit 1, a cylindrical lens 11, a polygon mirror 12, three fθ lenses 13, 14, 15, and a cylindrical lens 16, a plane mirror 17, a photosensitive drum, 25.

The light source unit 1 comprises a laser diode array 2 and a collimator lens 5. As shown in FIG. 2, the laser diode array 2 incorporates an edge-emitting laser diode element 3 having three light emitting points 3a, 3b, 3c. The light emitting points 3a to 3c are unequally spaced in the sub-scanning direction (described later). In the present embodiment, the distance between the light emitting points 3a and 3b is 12.7 μm,
The interval between b and 3c is set to 21.2 μm. Light beams B ₁ , B ₂ , emitted from the light emitting points 3a, 3b, 3c
B ₃ is converted into parallel light (or convergent light) by the collimator lens 5.

The light beams B _{1 to} B ₃ emitted from the collimator lens 5 reach the polygon mirror 12 via the cylindrical lens 11. Cylindrical lens 11
Focuses the light beams B _{1 to} B ₃ in the vicinity of the reflection surface of the polygon mirror 12 in a linear shape long in the main scanning direction. Polygon mirror 1
2 is driven to rotate at a constant angular velocity in the direction of arrow a. The light beams B _{1 to} B ₃ are deflected and scanned at equal angular velocities on the respective reflecting surfaces based on the rotation of the polygon mirror 12, and the fθ lenses 13, 1
4 and 15 and the cylindrical lens 16 and are reflected downward by the plane mirror 17. Then, the light beam B ₁
With .about.B ₃ is imaged on the photosensitive drum 25, an arrow b
Scan in the direction.

Lenses 13, 14, and 15 correct the main scanning speed on the photosensitive drum 25 of the light beams B _{1 to} B ₃ deflected at an equal angular velocity by the polygon mirror 12 at an equal speed (distortion aberration correction). Has a function. The cylindrical lens 16 has power only in the sub-scanning direction similarly to the cylindrical lens 11, and the two lenses 11 and 16 cooperate to correct a surface tilt error of the polygon mirror.

The photosensitive drum 25 is driven to rotate at a constant speed in the direction of arrow c, and the polygon mirror 12 and the fθ lens 1 are rotated.
An image (electrostatic latent image) is written on the photosensitive drum 25 by main scanning in the direction of arrow b by 3, 14, and 15 and sub-scanning of the photosensitive drum 25 in the direction of arrow c. Next, writing of an image on the photosensitive drum 25 by the two-beam scanning optical device capable of switching the image density will be described with reference to FIGS.
This will be described with reference to FIG.

As shown in FIG. 3A, the light emitting points 3a, 3a
b, light beam B emitted from 3c ₁, B_Two, B_ThreeIs the feeling
Beam spots are placed on the optical drum 25 at unequal intervals in the sub-scanning direction.
The cuts 8a, 8b, 8c are formed. Beam spot 8a
And 8b spacing is required from 400 dpi image density
The light beam interval is 63.5 μm. Beam spot 8
The interval between b and 8c is required from the image density of 240 dpi.
The light beam interval is 105.8 μm. And exposure
Forming an image with an image density of 400 dpi on the body drum 25
When the light emitting point 3a and the light emitting point 3b are turned on,
3c is not turned on. In this case, on the photosensitive drum 25
As shown in FIG. 3 (B), the distance of 63.5 μm
Two beam spots 8a and 8b are formed. This bee
As shown in FIG. 4, the scanning spots 8a and 8b
Are scanned in order from the image front end.

Next, the image density is increased from 400 dpi to 240
When switching to dpi and forming an image of 240 dpi, the light emitting point 3a is not turned on, but the light emitting point 3b and the light emitting point 3c are turned on. In this case, as shown in FIG. 3C, two beam spots 8b and 8c having an interval of 105.8 μm are formed on the photosensitive drum 25. The scanning lines are sequentially scanned by the beam spots 8b and 8c from the front end of the image. Further, when switching the image density from 400 dpi to 240 dpi, the rotation speed of the photosensitive drum 25 or the deflection speed of the polygon mirror 12 is changed in accordance with the image density. Alternatively, the photosensitive drum 25
And the deflection speed of the polygon mirror 12 are changed.

Here, the control circuit block for switching the image density, as shown in FIG. 5, roughly controls the RAM 61 for storing image data and the light emitting points 3a to 3c of the laser diode array 2. Light emitting point controller 62, drivers 63a, 63b, 63c for driving light emitting points 3a, 3b, 3c, and polygon mirror 1
2, a speed controller 64 for controlling the deflection speed of the photosensitive drum 25 and the rotation speed of the photosensitive drum 25, a driver 65 for rotating and driving the polygon mirror 12, and a photosensitive drum 2
And a driver 66 for rotating the drive 5.

For example, when the light beam scanning optical device of the present embodiment is incorporated in a digital copying machine, an image density changeover switch is provided on the operation panel surface of the copying machine, and a signal input from the image density changeover switch is used.
The image density of the light beam scanning optical device can be controlled. In this case, if the operator selects, for example, an image of 400 dpi using the image density changeover switch, an image density signal is transmitted from the host computer 60 to the light emitting point controller 62 and the speed controller 64. The speed controller 64 transmits a control signal to each of the drivers 65 and 66 so that a predetermined deflection speed and rotation speed can be obtained based on the image density signal. Each driver 6
5 and 66 respectively drive the polygon mirror 12 and the photosensitive drum 25 at a deflection speed and a rotation speed corresponding to the image density.

On the other hand, the light emitting point controller 62 transmits a driver ON / OFF signal to the drivers 63a to 63c based on the image density signal, and sets the drivers 63a and 63b to O.
N state, and the driver 63c is turned off. Next, when a command signal from the host computer 60 is input to the RAM 61 via the interface (I / F), the image data stored in the RAM 61 is sequentially extracted and transmitted to the controller 62. The controller 62 converts the respective image data into drivers 63a and 63b.
And the drivers 63a and 63b drive the corresponding light emitting points 3a and 3b.

As described above, the three light emitting points 3 a to 3 of the laser diode array 2 are controlled by the light emitting point controller 62.
c, any two light-emitting points are selected from among the light-emitting points, and the speed controller 64 changes the deflection speed of the polygon mirror 12 and the rotation speed of the photosensitive drum 25 to change the light beam interval on the photosensitive drum 25. Can be accurately changed. Thus, it is possible to easily switch the image density and obtain an image with excellent image quality without providing a movable mechanism for switching the image density.

The light beam scanning optical device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. As shown in FIG. 6, for example, photoconductors 503C, 503M, and 503 for cyan, magenta, yellow, and black, respectively.
The present invention is also effectively applied to a tandem-type light beam scanning optical device in which Y and 503Bk are arranged in a row facing a transfer belt. In FIG. 6, reference numeral 500 denotes a transfer belt.

Further, as shown in FIG.
05, the photosensitive drum 506, and the photosensitive drum 506
Developing units 507C, 507 for cyan, magenta, yellow, and black disposed around
The present invention is also effectively applied to a light beam scanning optical device of a type including M, 507Y, and 507Bk.

The light emitting points need only be arranged at different positions in the sub-scanning direction, and need not necessarily be one-dimensionally arranged in parallel with the sub-scanning direction as in the above-described embodiment. For example, the light emitting points may be arranged one-dimensionally in a direction inclined with respect to the sub-scanning direction, or the light emitting points may be arranged two-dimensionally. Further, the light emitting point intervals of the light source may be equal intervals in the sub-scanning direction, and the light source may be a surface emitting laser diode element in addition to the edge emitting laser diode element.

[0021]

As is apparent from the above description, according to the present invention, the light emitting point is switched by the light emitting point switching means in accordance with the desired image density, and the deflection speed of the deflector is changed by the speed converting means. By changing at least one of the moving speeds of the scanned surface, the image density can be easily switched without providing a movable mechanism, and an image with excellent image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a light beam scanning optical device according to the present invention.

FIG. 2 is a perspective view showing a laser diode element incorporated in the laser diode array.

3A is an explanatory diagram showing a beam spot interval on a photosensitive drum, FIG. 3B is an explanatory diagram for forming an image at 400 dpi, and FIG. 3C is an explanatory diagram for forming an image at 240 dpi. FIG.

FIG. 4 is an explanatory diagram showing scanning when forming a 400 dpi image.

FIG. 5 is a control circuit block diagram for switching an image density.

FIG. 6 is a schematic configuration diagram showing another type of a light beam scanning optical device according to the present invention.

FIG. 7 is a schematic configuration diagram showing still another type of a light beam scanning optical device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source unit 2 ... Laser diode array 3 ... Laser diode element 3a, 3b, 3c ... Light emitting point 5 ... Collimator lens 8a, 8b, 8c ... Beam spot 12 ... Polygon mirror 13, 14, 15 ... Scanning lens 25 ... Photoconductor drum 60 ... host computer 61 ... RAM 62 ... emission point controller 63 a to 63 c ... driver 64 ... speed controller 65, 66 ... driver _{B 1, B 2, B 3} ... light beam

Claims (2)

[Claims] 1. A light source having at least three light emitting points arranged at different positions in a sub-scanning direction, and light emitting point switching means for selecting two light emitting points from the light emitting points to emit light in order to switch image density. A deflector that deflects and scans a light beam emitted from the light source; a scanned surface that is irradiated with the light beam and moves in a sub-scanning direction; and a light beam that is emitted from the deflector is placed on the scanned surface. A scanning optical element for scanning in a line shape, and speed changing means for changing at least one of the deflection speed of the deflector and the moving speed of the surface to be scanned in order to switch the image density. A light beam scanning optical device characterized by the following. 2. The light beam scanning optical device according to claim 1, wherein the light emitting point intervals of the light source are unequal in the sub-scanning direction.